Synchronization of unstable signal sources for use in a phase stable instrument

ABSTRACT

A vector network analyzer (VNA) can include a control processor, a plurality of receivers coupled with the control processor, the plurality of receivers having a common signal generator source, and a coupler/power divider network configured to distribute each of a plurality of source reference signals to a corresponding one of the plurality of receivers.

TECHNICAL FIELD

The present disclosure relates generally to electronic test andmeasurement devices, such as Vector Network Analyzers (VNAs), VectorSignal Analyzers, Spectrum Analyzers, Vector Signal Generators, andsignal generators.

BACKGROUND

In prior instruments, such as a tracking generator or vector networkanalyzer (VNA), a plurality of phase-stable measurements of a deviceunder test (DUT) reflection and/or transmission must be made. Single ormultiple generators and receivers share a common local oscillator (LO)to assure phase stability. Calibration of the system is performed usingexternal reflection standards, which rely on coherent phase between thecalibration moment and the measurement moment. For reasons of costreduction and simplification of the hardware, it would be desirable touse phase-incoherent but frequency-stable LO sources for the receiverand generator rather than sharing a common synthesizer architecture. Thecommon VNA has a reflection bridge or coupler arrangement of varioustypes on the generator port. A signal reference coupled from thegenerator is routed to the receiver but has a phase error that isproportionate to the reflection coefficient of the(arcsin(V_(ref)/V_(norm))), making the reference generator phaserelative to the receiver difficult to obtain from this port alonewithout relying on the phase coherence of a common LO system between thegenerator and receiver.

FIG. 1 is a block diagram illustrating an example of a prior vectornetwork analyzer (VNA) or tracking generator 100 having multiplereceivers 110 and 112 and a shared signal 125 (e.g., from a controlprocessor 120 by way of an LO 116). In the example, a common source 102provides an injection signal to a radio frequency (RF) bridge 106 (e.g.,via a transmission line 104), as well as reference signals 107 a and 107b to multiple receivers 110 and 112, respectively.

It should be noted that, while two receivers 110 and 112 are shown tomeasure two signals (e.g., Reference and Reflection ports of a bridge),any number of multiple receivers can be used to measure a high number ofsignals from more complex multi-channel bridges, couplers, or similarnetworks. Multiple receivers can be eliminated with a single receiver ifa phase-stable switch can be connected in such a way that the bridgeloading is not disturbed when the paths are switched.

FIG. 2 is a block diagram illustrating an example of a prior VNA ortracking generator 200 having a single receiver 210 and a shared signal225 (e.g., from a control processor 220 by way of an LO 216). Similar tothe VNA or tracking generator 100 illustrated by FIG. 1, a common source202 provides an injection signal to a radio frequency (RF) bridge 206(e.g., via a transmission line 204), as well as reference signals 207 aand 207 b to switching circuitry 209 that is coupled with the receiver210. In general, the shared signal may be the bridge stimulus itself oran LO created in a phase stable way within the signal source.

SUMMARY

Implementations of the disclosed technology generally include systems ordevices that use an additional signal path in order to allow for arelative phase measurement between a generator and a receiver,insensitive to external load conditions. Such embodiments mayadvantageously allow a receiver and generator having relatively unstableindependent local oscillators (LOs) to be used in a phase-stablemeasurement of network response. This may advantageously allow a singlereceiver and generator to establish their relative phase or, inembodiments involving multiple receivers and multiple generators, toestablish their relative phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of a prior vectornetwork analyzer (VNA) or tracking generator having multiple receiversand a shared signal.

FIG. 2 is a block diagram illustrating an example of a prior VNA ortracking generator having a single receiver and a shared signal.

FIG. 3 is a block diagram illustrating an example of a VNA or trackinggenerator having a calibration path in accordance with certainimplementations of the disclosed technology.

FIG. 4 is a block diagram illustrating an example of a VNA or trackinggenerator having a common generator source in accordance with certainimplementations of the disclosed technology.

FIG. 5 is a block diagram illustrating a first example of a VNA ortracking generator having multiple receivers that are synchronized by acommon reference signal in accordance with certain implementations ofthe disclosed technology.

FIG. 6 is a block diagram illustrating a second example of a VNA ortracking generator having multiple receivers that are synchronized by acommon reference signal in accordance with certain implementations ofthe disclosed technology.

FIG. 7 is a block diagram illustrating an example of a VNA or trackinggenerator having multiple signal sources that are synchronized by asingle receiver in accordance with certain implementations of thedisclosed technology.

DETAILED DESCRIPTION

Implementations of the disclosed technology generally include electronictest and measurement devices, such as vector network analyzers (VNAs)having a calibration path. Such embodiments may advantageously includeseparate signal sources in the receiver(s) and signal source to allowfor higher stability and accuracy in the bridge measurement. Also,variable static phase offsets in either the receive synthesizer orsource synthesizer may be sensed and removed as an error term in themeasurement. Further, costs may be reduced due to the availability ofsingle integrated circuit (IC) integrated synthesizers that cover widebandwidths at low cost.

FIG. 3 is a block diagram illustrating a first example of a VNA ortracking generator 300 having a load 302, a transmission line 304, aradio frequency (RF) bridge 306 provide reference signals 307 a and 307b to switching circuitry 309, and a calibration path in accordance withcertain implementations of the disclosed technology. In the example, aseparate signal source 325 (e.g., by way of a generator 321, an LO 317,and a switch 314) and receive reference 326 are shown with a phase shift315 shown in series with the signal source to represent the random phaseoffset to the receive channel. Each of the signal sources is phaselocked to a common reference and controlled by a common controlprocessor 320, and the signal source may have an unknown phase. While asingle receiver 310 is shown, it should be noted that multiple receiversmay be synchronized using similar implementations.

In the example, the signal channel generator 321 has a single channelreceiver for sensing the magnitude and phase of a single reflectionbridge/coupler 306, e.g., used in a one-port VNA. The generator 321 andreceiver 310 may use either continuous wave or modulated data. Thereceiver(s) may be constructed each having an independent localoscillator, e.g., with independent phase. The phase offset 315 from thesource may be determined by sampling the “source Reference path.” Here,Si may either refer to a switch or a coupling or power dividing network.In embodiments where a single receiver is used to sample a single portor multiple bridge ports, the switch may be designed to provide aconsistent load to the bridge in all switch positions. This may beaccomplished using signal path attenuation, impedance matching,buffering by amplification, and terminated switch networks, for example.

FIG. 4 is a block diagram illustrating an example of a VNA or trackinggenerator 400 having a common generator source (e.g., from a controlprocessor 420 by way of an LO 317) in accordance with certainimplementations of the disclosed technology. In the example, multiplereceivers 410, 411, and 412 having independent LOs 410 a, 411 a, and 412a, respectively, and multiple phase offsets may be synchronized to acommon reference. In this view, the multiple source reference signalsare distributed by way of a coupler/power divider network 445. Inalternate embodiments, a switch may be implemented instead of thecoupler/power divider network 445.

In the example, the receivers 410-412 and generators can be phasesynchronized by tuning each to the same frequency, switching to the“Source Reference” signal, and measuring the relative phase. Frequencyoffsets between the source and receivers may be accommodated if thesesignals are within the processing bandwidth of the receivers 410-412. Itshould be noted that the receivers 410-4112 are generally analog ordigital receivers with superheterodyne, homodyne, direct conversion, orsimilar receiver techniques. Single or multiple LO signals may begenerated by each receiver. For example LO 1 (410 a) may be actuallythree LO signals (e.g., LO1 a, LO2 b, and LO1 c for a three-stagesuperheterodyne converter). The generator may either be a direct signalsource (e.g., a VCO and PLL, direct digital source, or direct analogsource) or an indirect signal source (e.g., with a local oscillator andbaseband signal, or multiple location oscillators and a basebandsignal), with either a modulated or continuous wave baseband signal.

FIG. 5 is a block diagram illustrating a first example of a VNA ortracking generator 500 having multiple receivers that are synchronizedby a common reference signal in accordance with certain implementationsof the disclosed technology. In the example, a single control processor520 may control multiple receivers 510, 511, and 512 having independentLOs 510 a, 511 a, and 512 a, respectively with random phase offsets. NSource reference signals are routed from a single generator. Whilesimplified signal source is shown in the figure, this signal source maybe an indirect signal source (e.g., with a local oscillator and basebandsignal, or with multiple LOs and a baseband signal) with either amodulated or continuous wave baseband signal or a direct signal sourcesuch as a VCO and PLL, direct digital source, or direct analog source.The phase offset represents random phase offset that may be presentbetween each receiver and the generator.

FIG. 6 is a block diagram illustrating a second example of a VNA ortracking generator 600 having multiple receivers that are synchronizedby a common reference signal in accordance with certain implementationsof the disclosed technology. In the example, synchronizer circuitry 601consists of a signal source (Gen1), a common reference clock (e.g.,which produces 10 MHz 1 . . . 10 MHz N outputs to synchronize n externalspectrum analyzers 610, 611, and 612), a 10 MHz or other suitable signalto synchronize the reference generator “Gen 1”, signal routing andswitching circuitry 610 a, 611 a, and 612 a, respectively, to eachspectrum analyzer RF input, and N-RF inputs. Signal 1 to Signal n inputsto the control processor 620 may include several USB data signals or anyother common data bus, such as USB/PXI/VXI etc.

FIG. 7 is a block diagram illustrating an example of a VNA or trackinggenerator 700 having multiple signal sources that are synchronized by asingle receiver in accordance with certain implementations of thedisclosed technology. In the example, generator channel SPDT switchesmay be of internal-terminated form when the path is open. The stabilityof bridge response during switching may be improved using buffors,amplification, attenuation, or other suitable mechanisms. Signal 1 maybe modulated or a continuous wave signal. The signal source may be adirect source of heterodyne source. The phase offset of each generatormay be sensed relative to the others by way of a common receiver, forexample.

Having described and illustrated the principles of the invention withreference to illustrated embodiments, it will be recognized that theillustrated embodiments may be modified in arrangement and detailwithout departing from such principles, and may be combined in anydesired manner. And although the foregoing discussion has focused onparticular embodiments, other configurations are contemplated.

In particular, even though expressions such as “according to anembodiment of the invention” or the like are used herein, these phrasesare meant to generally reference embodiment possibilities, and are notintended to limit the invention to particular embodiment configurations.As used herein, these terms may reference the same or differentembodiments that are combinable into other embodiments.

Consequently, in view of the wide variety of permutations to theembodiments that are described herein, this detailed description andaccompanying material is intended to be illustrative only, and shouldnot be taken as limiting the scope of the invention. What is claimed asthe invention, therefore, is all such modifications as may come withinthe scope and spirit of the following claims and equivalents thereto.

1. A vector network analyzer, comprising: a control processor; aplurality of receivers coupled with the control processor, the pluralityof receivers having a common signal generator source from the controlprocessor; and a coupler/power divider network configured to distributeeach of a plurality of source reference signals to a corresponding oneof the plurality of receivers.
 2. The vector network analyzer of claim1, wherein each of the plurality of receivers has an independent localoscillator (LO).
 3. The vector network analyzer of claim 2, wherein atleast one independent LO is configured to generate multiple LO signals.4. The vector network analyzer of claim 1, wherein each of the pluralityof receivers is one of a group consisting of: a superheterodynereceiver, a homodyne receiver, and a direct conversion receiver.
 5. Thevector network analyzer of claim 1, wherein the common signal generatorsource is a direct signal source.
 6. The vector network analyzer ofclaim 5, wherein the direct signal source is one of a group consistingof: a voltage controlled oscillator (VCO) and a phase-locked loop (PLL).7. The vector network analyzer of claim 5, wherein the direct signalsource is one of a group consisting of: a direct digital source and adirect analog source.
 8. The vector network analyzer of claim 1, whereinthe common signal generator source is an indirect signal source.
 9. Thevector network analyzer of claim 8, wherein the indirect signal sourceis one of a group consisting of: a single LO with a baseband signal andmultiple LOs with a baseband signal.
 10. A vector network analyzer,comprising: a control processor; a receiver coupled with the controlprocessor; switching circuitry coupled with the receiver; a radiofrequency (RF) bridge coupled with the switching circuitry; atransmission line coupled with the RF bridge, wherein the transmissionline is configured to be coupled with a load; and a signal generatorcoupled with the RF bridge.
 11. The vector network analyzer of claim 10,wherein the RF bridge is configured to provide a plurality of referencesignals to the switching circuitry.
 12. The vector network analyzer ofclaim 10, wherein the signal generator is configured to provide a sourcesignal to the RF bridge.
 13. The vector network analyzer of claim 10,further comprising a local oscillator (LO) coupled with the receiver.14. The vector network analyzer of claim 10, further comprising a localoscillator (LO) coupled with the signal generator.
 15. The vectornetwork analyzer of claim 14, further comprising a switch coupled withthe signal generator and configured to switch between the RF bridge andthe receiver.
 16. The vector network analyzer of claim 14, wherein thecontrol processor is configured to phase lock the signal generator to acommon reference.